Tube or bar stock feed systems which convey such material in its longitudinal direction have been used in the material handling field and in the field of non-destructive testing. A rather complex roller assembly used in a roller conveyor which can effect longitudinal displacements of elongate elements of various cross-sectional shapes and dimensions is illustrated in U.S. Pat. No. 2,860,766 to Welter. A more common but less versatile form of roller assembly is disclosed in British Pat. No. 1,124,350 to Busche et al. It comprises a pair of coaxial frusto-conical rollers which form a split roller assembly. While a series of such rollers, especially when mounted on a shaft which is rotationally driven, may form a conveyor, this conveyor may not be useful for applications in which it is desired that tube or bar stock of various cross sectional shapes and sizes be maintained on a constant center in two mutually perpendicular directions which are perpendicular to the direction of transport of the material. Where the adjustment of roller position with respect to a center has been provided in the prior art each roller assembly would have to be individually adjusted. This made alignment of a conveyor which comprises a series of roller or drive assemblies a tedious, difficult and time consuming process requiring skill or special techniques. The adjustment process has generally been carried out manually on each roller assembly rather than automatically.